Purifying light-metal alloys



Patented Apr. 15, 1930 UNITED STATES PAT E'NT OFFICE JOHN A. GANN, ,OI MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN PUBIIYING LIGHT-METAL ALLOYS R Drawing.

As is Well known, crude magnesium is often very impure, the impurities consisting I largely of' non-metallic ingredients, and

where it is attempted toremelt shavings-of a the metal or other scrap magnesium metal, it

is equally important that steps be taken to eliminate the foreign matters, if clean cast ings are to be secured either in the form of stock bars or finished articles.

The object of the present invention accordin ly is the PIOVlSlOIl of an improved method for eliminating such impurities either in the case of magnesium metal or of so-called light metal alloys in which magnesium is the predominant ingredient;

To the accomplishment of the foregoing and related ends the invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims, the following description setting forth but one of the various ways in which the principle of the invention may be carried out.

The main st'ep'in my improved process consists in the washing or thorough intermixture of the metal or such alloy thereof while in molten condition with a suitable fluxing material. Several different fluxes have been described and used either in connection with the electrolytic production of magnesium or as a coating for the metal in molten state in order to protect the'same against oxidation which becomes excessive where the molten metal is exposed directly to the atmosphere. Anhydrous magnesium chloride, which is one of the materials employed in the electrolytic production of the metal, serves also when in molten. condition as a flux or protective coating but has too high a melting point so that sodium chloride is ordinarily added to lower such melting point. The flux thus composed of magnesium chloride and sodium chloride is disclosed in U. S. Patent No. 1,37 7 ,374 and also in German Patent No. 122,312, the latter describing a flux consisting of equimolecular weights of magnesium chloride, sodium chloride and potassium chloride with the addition of a small amount of calcium fluoride. Another flux that has been found to work successfully in commer- 50 cial practice consists of a mixture of mag Application filed July 13, 1923. Serial No. 651,431.

nesium and sodium chlorides in approximately equal pro ortions with a relatively small amount of b raise the specific gravity of the flux slightly above that of the metal, either magnesium alone or an alloy thereof, with which it is to be used.

In the ractice of my present improved method 0 purification an of the foregoing fluxes may be employed m which the proportion of ingredients is such that the melting oint of the mixture is lower than that of t e metal or alloy and at the same time such flux mixture, when in molten state, has a surface tension sufiicient to cause it to coat the exposed surface of the metal. Such flux will also preferably have a slightly higher specific gravity'than the metal or alloy so that the latter will float in a bath of the flux and separated particles of the metal will be caused to coalesce. W A batch of the metal or alloy containing impurities as aforesaid is melted down in a pot containing a sufficient quantity of such flux material to float and effectively coat the body of metal when in molten state. According to the preferred procedure, the flux employed at this stage is that resulting from arium chloride added to- Y a subsequent step in the purification treatment as will presently appear. As soon as i the metal is in proper fluid state, the flux of course being likewisefluid at the temperature necessarily involved since, as stated, such flux is composed of ingredients that will melt at a lower temperature than the metal, the latter is agitated or stirred with the flux so as to be thoroughly intermixed therewith whereupon the mixture is allowed to stand in a quiet condition. This intermixture of the metal and flux with subsesium or its alloy and the metal is then in suitable condition for casting.

The purified body of metal, or at least the major portion thereof, obtained as a result of 5 the last ste is transferred directly from the pot to suita le molds, leaving behind the flux with the im urities taken up thereby from such body of metal. This flux is then used in repeating the first step wherein the crude metal with maximum content of impurities is melted down and agitated as hereinbefore set forth. None of the metal from the second step that is left in the flux bath is of course lostsince itis mingled with the raw metal thus added in repeating the first step. In order to ladle the metal from one pot to the other, the thin film of the flux that overlies the surface of the molten mass of metal in the pot is broken and brushed to one side so as to uncover the clear metal and the ladle can then be filled and lifted before the film is reestablished. However, where proper precautions are taken, such reestablishment of the film will occur before any oxidation or other harmful effect is produced on the exposed metal and by careful manipulation the o erator is at the same time able to avoid tal ing up any of the flux in the ladle. It will be understood, of course, that the-method of purification in hand is not limited to anysuch particular method of transferring the metal. It will also be understood that I may increase-the number of successive operations wherein progressively cleaner flux is employed instead of operating simply in two stages as described.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the method herein disclosed, provided the step or ste s stated by any of the following claims or t e equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention 1. A method of purifying magnesium and alloys thereof, which comprises washing the molten metal by agitating and intermingling in a molten bath of a suitable flux and then separating.

2. A method of purifying magnesium and alloys thereof, which comprises washing the metal by successively agitating the molten metal in a molten bath of a suitable flux, and

allowing the metal and flux to stand after each such agitating step until the metal has substantially separated from the flux.

3. A method of purifying magnesium and alloys thereof, whichcomprises washing the metal by successively agitating the molten metal in a. molten bath of a suitable flux at least a portion of which is substantially anhydrous magnesium chloride, and

6 allowing the metal and flux to stand after each such agitating step until the metal has substantially separated from the flux.

4. A method of purifying magnesium and alloys thereof, which comprises washing the metal by successively agitating the molten metal in a molten bath of a suitable flux containing substantially anhydrous magnesium chloride and sodium chloride, and allowing the metal and flux to stand after each such agitating step until the metal has substantially separated from the flux.

5. A method of purifying magnesium and alloys thereof, which comprises washing the metal by agitating the molten metal in a bath of a suitable flux that has been previously used in a similar step, and then agitating the metal with comparatively clean flux.

6. A method of purifying magnesium and alloys thereof, which compriseswashing the metal by successively agitating the molten metal in baths of suitable flux progressively cleaner of impurities.

7 A method of purifying magnesium and alloys thereof which comprises washing the metal by agitating the molten metal in a bath of a suitable flux that has been previously used in a similar step, allowing such metal and flux to stand until the metal has substantially separated from such flux, then agitating the metal in comparatively clean flux, again allowing the metal and flux to stand until the metal has substantially separated from the flux, and utilizing such flux for another batch of metal. 1

8. A method of purifying magnesium and alloys thereof, which comprises agitating the metal in molten condition in a relatively large liquid bath of flux, and separating the metal from the liquid bath.

Signed by me, this 5th day of July, 1923.

JOHN A. GANN. 

